A gas generated in a coke oven contains ammonia of 6 to 10 g/Nm.sup.3, and it must be removed since it causes corrosion in pipings of the coke oven gas (called as "COG" hereinafter) and generates NOx at combustion of COG. As methods of removing ammonia from COG, in general COG is washed with dilute sulfuric acid and ammonium sulfate is recovered. However, this method is very poor in payability, because fertilizers of ammonium sulfate have been very little required nowadays, and a market price has largely fallen accordingly, and the treatment of ammonia by the production of ammonium sulfate is not valuable industrially. Presently, the production of ammonium sulfate has been cut down, and there are other ammonia treatments, for example, Phosam method which produces liquid ammonia of high purity; Koppers method which separates ammonia and burns it directly; or Carl Still method which burns ammonia under the presence of a catalyzer. But, since these methods are not perfectly satisfactory, either, in view of economical treatments, various improvements have been attempted, and at the same time new processes of ammonia treatments have been developed vigrously.
Under these circumstances, the inventors developed and proposed a treating method of ammonia recovered from COG, which comprised, burning ammonia catalytically under the presence of air to change into nitrogen and water, decomposing it catalytically by a heat caused by said burning, and recovering hydrogen.
There have been up to now submitted many reports with respect to catalyzers useful to ammonia decomposition. For example, "CATALYSIS Science and Technology" describes, vol. 1, page 118 (1981), useful catalysis elements such as molybdenum, tungsten, rhenium, iron, ruthenium, cobalt, rhodium, nickel, platinum, copper and vanadium.
The ammonium decomposition has been utilized industrially to production of an atmospheric gas to be used to brighten annealings of stainless steel or nickel steels and the catalyzers thereof are Fe.sub.2 O.sub.3 -Al.sub.2 O.sub.3, NiO-SiO.sub.2 .multidot.Al.sub.2 O.sub.3 and Pt-Al.sub.2 O.sub.3. These catalyzers are used at space velocity of 500 to 1000ml/ml.h and at temperatures of 500 to 900.degree. C., substantially 700 to 1200.degree. C. But, foregoing catalyzers such as Fe.sub.2 O.sub.3 -Al.sub.2 O.sub.3, NiO-SiO.sub.2 .multidot.Al.sub.2 O.sub.3, pt-Al .sub.2 O.sub.3 and Ru-Al.sub.2 O.sub.3 have problems as mentioned under, requiring high temperatures as 700 to 1200.degree. C. for decomposing ammonia perfectly:
(1) Heat resistant materials are required for reactors. PA0 (2) Energy is much consumed for maintaining reaction temperature high.
The present invention has been developed for settling these problems about the prior art, and is to propose a catalyzer for decomposing ammonia into hydrogen and nitrogen at low temperature ranges.